This invention relates generally to turbine engine combustors and, more particularly, to turbine engine combustor members including an inner surface exposed directly to the combustor interior and the combustion of fuel.
During operation of a turbine engine, for example a gas turbine engine, ambient air flows into a compressor that discharges compressed air to a combustor of a combustion system. A mixture of the compressed air and fuel is ignited in the combustor to provide pressurized combustion products to a downstream turbine system that extracts energy from the combustion products for a designed operation of the engine. A variety of turbine engine combustion systems and components have been reported, for example in U.S. Pat. No. 5,117,624—Roberts, Jr. et al.; U.S. Pat. No. 5,289,687—Kress et al.; and U.S. Pat. No. 5,355,668—Weil et al.
As is well known in the gas turbine engine art, temperatures as a result of such combustion within the interior of the combustor can be as high as about 3000° F. In addition, because of the presence of oxygen in a rapidly flowing fluid stream, inner surfaces of combustor members exposed to the combustion of fuel and compressed air are subject to very strenuous high temperature hot corrosion and oxidizing conditions. Examples of such combustor members include those referred to in the art as deflectors (sometimes called splash plates, baffles or heat shields), center bodies, swirl cups, and combustor liners and liner segments, each including a surface exposed to the combustor interior in which combustion occurs during operation. Because of such operating conditions, it has been a practice to manufacture combustor members, that include at least one inner surface exposed to such temperatures and conditions, from alloys having high temperature resistant properties and to coat such inner surfaces with a high temperature environmental resistant coating or coating system. Sometimes cooling air is applied to or through members to reduce operating temperatures of the members. Typically, some of such combustor members have been coated individually and then assembled with other associated components into a combustor.
One example of a combustor member of particular interest is a deflector mounted to an axially forward dome structure through which compressed air and fuel are introduced into the combustor. The deflector is mounted to the dome structure hot or interior side to provide a barrier or heat shield from hot gas radiation and convection. Fuel discharging to the combustion zone from a swirler cup exit or flare often films along deflector faces resulting in stagnation or recirculation zones at deflector outer edges. High fuel-air ratios in such recirculation zones can hold a combustion flame on the deflector edges. This can result in local gas temperatures sufficiently high to cause rapid oxidation or melting of the deflector edges as well as to provide an environment conducive to hot corrosion on other surfaces of the deflector. Similar results have been observed on another example of a combustor member called a hollow center body that acts to partially define inner and outer annular combustor portions in one form of an annular combustor system.
Environmental protective coating combinations that have been applied to surfaces of combustor members exposed to such conditions include an inner or bond coating of a well known and widely reported MCrAl-type base material in which the M represents at least one of the elements Fe, Co, and Ni. Such base materials have been reported to include additional elements such as at least one of Y, Hf, Pt, Rh, Si, Zr, and others. One typical example is a NiCrAlY coating. U.S. Pat. No. 4,897,315—Gupta presents some background and examples of knowledge of MCrAl-type coating materials. It has been a practice to use an MCrAl-type coating as a bond coat for an outer ceramic-base thermal barrier coating (TBC) one form of which is a coating based on zirconia stabilized with about 3–20 weight % yttria, typically, by weight, about 92% zirconia stabilized with about 8% yttria. This general type of coating system is discussed in such U.S. Patents as U.S. Pat. No. 5,771,577—Gupta et al. One manufacturing advantage of use of such coating combination is that the bond coat and outer ceramic TBC can be applied by a commercially available method called Air Plasma Spray (APS).
Another more costly protective coating system that has been applied to combustor members is an aluminide diffused with Pt to provide a PtAl inner coating. The above-described TBC then has been deposited over the PtAl coating by electron beam plasma vapor deposition (EB-PVD). Current deflectors are coated individually on at least one surface, including inner surfaces exposed to combustion of fuel, and sometimes on outer surfaces away from the combustor interior before assembly. Therefore, a PtAl/TBC type of coating has been used in combination with an advanced high temperature alloy having good high temperature oxidation resistance to provide a component with enhanced operating performance.
Provision of a combustor component, for example a deflector, made of an improved high temperature alloy having not only good oxidation resistance but also excellent, improved hot corrosion resistance requires, at most, application of a high temperature environmental coating only to surfaces exposed to a combustor interior. This can enable assembly of the component with other members of a combustor prior to coating and then coating, with any appropriate masking, of the entire assembly rather than of individual components. Such a combination of materials and processes enhances operating performance of the combustor while reducing manufacturing cost.